The present invention relates to multi-axis apparatus and methods for internal spinal fixation. In more detail, the present invention relates to a connection for an internal spinal fixation system, and a method of stabilizing, or fixing, the spine, utilizing multiple axes for transferring load from the patient's spinal column to the stabilizer.
Treatment of a damaged or diseased intervertebral disk continues to be a challenging field of medicine. The classical treatment for a damaged or diseased disk is removal of all or a portion of the disk from between the vertebrae. However, removing the disk increases the instability of the spine. If only a portion of the disk is removed, the intervertebral disk space is commonly filled with a bone plug or prosthetic device and the space around the plug or the implant is packed with bone chips to promote fusion of the adjacent disks, thereby increasing spinal stability. However, depending upon the particular pathology of the patient, partial diskectomy and fusion is not always indicated and problems relating to the failure of the bone chips to fuse and other complications of this surgery are well documented.
It is also known to use internal spinal stabilizers to address certain pathologies involving instability of the spinal column. Such stabilizers are utilizing in the thoracic and lumbar regions of the spine where the approach is from the patient's dorsal aspect. In the cervical region, a ventral approach (from the patient's front) presents the opportunity to use an internal stabilizer which is not nearly as affected by the problem of effective load transfer from vertebrae to stabilizer through the screw attaching the stabilizer to the vertebrae that characterize internal stabilizers implanted (dorsally) in the thoracic and lumbar region. Although not limited to this application, a spinal stabilizer incorporating the multi-axis connection of the present invention is intended for use in stabilizing the spinal column in the cervical region where effective load transfer may not be as complicated as with stabilizers intended for use in the thoracic and lumbar regions of the spine, but where load transfer is just as critical such that the stabilizer must be capable of being securely affixed to the vertebrae adjacent the diseased or damaged disk. To do so, the screws that affix the stabilizer plate to the vertebrae must be angled (relative to the surface of the plate) as required by the shape and size of the vertebrae, the normal curvature of the spinal column, the number of vertebrae to be stabilized, the spacing between vertebrae, the pathology of the patient's spinal column, and the many other factors encountered by the surgeon that are unique to each and every patient and each and every surgery. The multi-axis connection is also adaptable for use in an internal spinal stabilizer that is affixed to the thoracic or lumbar regions of the spine by dorsal approach.
It is, therefore, an object of the present invention to improve the interface between the screw and the plate in those spinal stabilizers which are affixed to the vertebrae by a screw and in which the screws are angled and/or spaced at varying intervals.
Another object of the present invention is to provide flexibility of placement, angulation, spacing, and screw height for accommodating the screws that are utilized to affix the plate of such stabilizers to the vertebrae.
Another object of the present invention is to provide a multiple-axis connection for an internal spinal stabilizer that allows the screw to be angled relative to the plate and in accordance with the particular circumstances of the patient's anatomy and pathology but which still resists movement of the screw relative to the plate after the stabilizer has been affixed to the vertebrae by locking the head of the screw into the plate.
Yet another object of the present invention is to provide an internal spinal stabilizer incorporating a multi-axis connection that locks the head of the screw utilized for affixing the plate comprising the stabilizer to the plate so as to resist relative movement between the plate and the screw but which also allows the screw to be removed from the plate as may be needed for effective load transfer from the patient's vertebrae to the stabilizer when affixed to the vertebrae or in the event the stabilizer must be removed or replaced at a later date.
Another object of the present invention is to provide a method of transferring load from a patient's spinal column to the plate of a spinal stabilizer by screws extending from the plate into the vertebrae at any of a plurality of angles while retaining the screw to the plate.
Other objects, and the many advantages, of the present invention will be made clear to those skilled in the art by the following description of the preferred embodiments thereof.